Imaging system for vehicle

ABSTRACT

An imaging system for a vehicle includes an imaging sensor and a video display device. The imaging system generates an overlay that is electronically superimposed on the displayed images to assist a driver of the vehicle when executing a backup maneuver. The overlay has first, second and third overlay zones, with the overlay zones indicative of respective distance ranges from the rear of the vehicle to respective distances. As indicated to the driver viewing the video display screen when executing a backup maneuver, the first distance is closer to the rear of the vehicle than the second distance and the second distance is closer to the rear of the vehicle than the third distance. The first overlay zone may be a first color and the second overlay zone may be a second color and the third overlay zone may be a third color.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent application Ser. No. 12/677,539, filed Mar. 31, 2010, now U.S. Pat. No. 8,451,107, which is a 371 national phase filing of PCT Application No. PCT/US08/76022, filed Sep. 11, 2008, which claims the benefit of U.S. provisional application Ser. No. 60/971,397, filed Sep. 11, 2007, which is hereby incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to imaging or vision systems, particularly for vehicles which provide a vehicle operator with wide angle scenic information of an area immediately around the vehicle, such as rearward of the vehicle.

BACKGROUND OF THE INVENTION

A long felt need in the art of vehicle vision systems, such as rear-view systems, has been to provide an operator of a vehicle with wide angle scenic information of an area around the vehicle, such as directly rearward of the vehicle, when the vehicle is traveling in reverse. Neither interior rear-view mirrors nor side exterior mirrors allow for visibility of the area immediately rearward of the vehicle's bumper, which is the information most critical to the vehicle operator when backing up. Therefore, various camera-based rear view vision systems have been proposed to provide visibility of this blind spot.

It is also known to provide a graphic overlay on the displayed image of the rearward scene to enhance the driver's perception of the rearward field of view. Examples of such graphic overlays are described in U.S. Pat. Nos. 5,670,935; 5,949,331; 6,222,447; and 6,611,202, which are hereby incorporated herein by reference in their entireties.

Various camera-based rear vision systems for vehicles backing up have been proposed. In one form of these systems, a camera with a conventional, standard lens is located on the rearward portion of the vehicle to provide a view of the area behind the vehicle. However, standard lenses fail to capture a wide angle view of the area, thus failing to provide the vehicle operator with an image of the entire critical area directly rearward of the vehicle. In order to provide a wider angle view of the rearward area, a wide angle lens system may be used with the camera to capture the critical area. Examples of such systems are described in U.S. Pat. Nos. 6,922,292; 6,757,109; 6,717,610; 6,590,719; and 6,201,642, which are hereby incorporated herein by reference in their entireties.

SUMMARY OF THE INVENTION

The present invention is directed toward enhancing exterior visibility to the driver of a vehicle by providing an imaging system that provides a wide angle field of view of the area directly exteriorly of a vehicle, and that provides a graphic overlay superimposed on a displayed image to enhance the driver's viewing and understanding or cognitive awareness of the displayed image of the scene rearward of the vehicle and any object or objects detected therein. The present invention is directed towards enhancing the interpretation of visual information in a rearview vision system by presenting information in a manner which does not require significant concentration of the driver or present distractions to the driver.

The rearview vision system of the present invention has an image capture device or image sensor or camera positioned on the vehicle and directed rearwardly with respect to the direction of travel of the vehicle, and a display for displaying images captured by the image capture device. Image enhancement means may be provided for enhancing the displayed image, such as in the form of graphic overlays superimposed on the displayed image. Such graphic overlays may include indicia of the anticipated path of travel of the vehicle which is useful in assisting the driver in guiding the vehicle in reverse directions. The graphic overlays may be flashed or intermittently activated and/or displayed in different colors depending on a distance to a detected object rearward of the vehicle so as to provide a spectral cue and a spatial cue to the driver as the driver maneuvers the vehicle in a rearward direction. The graphic overlays may comprise graphic overlay segments extending upward and inward along the sides of the image so as to be indicative of segments extending rearward from the sides of the vehicle. The graphic overlay segments may be viewed by the driver as having a virtual height dimension to enhance the driver's cognitive awareness of the graphic overlays. The graphic overlay segments may be displayed as three dimensional graphic overlay segments having a virtual height and a virtual thickness.

The camera or image sensor of the imaging system may include or utilize a wide angle lens that is compact, durable and inexpensive to manufacture. The image sensor and lens assembly of the present invention thus may comprise a wide angle lens or lens assembly, such as a multi-element lens assembly having multiple optics to provide a wide angle field of view with reduced distortion. Optionally, the lens may include multiple optics, such as four to seven optic elements, with an outer element (the element at the rearwardmost end of the lens and exposed at the rear exterior of the vehicle) comprising a glass element and with at least one other element comprising a plastic aspheric element.

These and other objects, advantages, purposes, and features of this invention will become apparent upon review of the following specification in conjunction with drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an imaging device comprising an image sensor and lens in accordance with the present invention;

FIG. 2 is an image as displayed to a driver of the vehicle in accordance with the present invention;

FIG. 3 is another image as displayed to a driver of the vehicle and having a graphic overlay superimposed thereon in accordance with the present invention;

FIG. 4 is another image as displayed to a driver of the vehicle and having a graphic overlay superimposed thereon in accordance with the present invention;

FIG. 4A is a perspective side view of the vehicle and overlay of FIG. 4;

FIG. 5 is another image as displayed to a driver of a vehicle and having a trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 5A is a perspective side view of the vehicle and overlay of FIG. 5;

FIG. 6 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 6A is a perspective side view of the vehicle and overlay of FIG. 6;

FIG. 7 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 8 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 9 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 10 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 10A is a perspective side view of the vehicle and overlay of FIG. 10;

FIG. 11 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 11A is a perspective side view of the vehicle and overlay of FIG. 11;

FIG. 12 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention;

FIG. 13 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention; and

FIG. 14 is an image as displayed to a driver of a vehicle and having another trailer hitch graphic overlay superimposed thereon in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and the illustrative embodiments depicted therein, a wide angle imaging system provides an operator of a vehicle with scenic information of an area immediately exteriorly, such as rearwardly, of the vehicle, which may be an automobile, a light truck, a van, a large truck, a sport utility vehicle or the like. The imaging system includes an image capture device 12 (FIG. 1) having an imaging sensor and a lens or lens assembly 14 that functions to focus a rearward field of view at an imaging plane of the imaging sensor or camera. Images 16 (FIG. 2) are displayed on a display device or screen with reduced distortion to enhance the driver's viewing and understanding of the displayed images. The rearview imaging system includes an image processor for receiving data signals from the image capture device and superimposing the graphic overlay on the displayed image, as discussed below.

The imaging sensor for the vehicle vision system of the present invention may comprise any suitable sensor, and may utilize various imaging sensors or imaging array sensors or cameras or the like, such as a CMOS imaging array sensor, a CCD sensor or other sensors or the like, such as the types described in U.S. Pat. Nos. 5,550,677; 5,670,935; 5,760,962; 5,715,093; 5,877,897; 6,922,292; 6,757,109; 6,717,610; 6,590,719; 6,201,642; 6,498,620; 5,796,094; 6,097,023; 6,320,176; 6,559,435; 6,831,261; 6,806,452; 6,396,397; 6,822,563; 6,946,978; 7,038,577; and 7,004,606; and/or U.S. patent application Ser. No. 11/315,675, filed Dec. 22, 2005 and published Aug. 17, 2006 as U.S. Patent Publication No. US-2006-0184297; and/or Ser. No. 10/534,632, filed May 11, 2005 and published Aug. 3, 2006 as U.S. Patent Publication No. US-2006-0171704; and/or U.S. provisional application Ser. No. 60/845,381, filed Sep. 18, 2007; and Ser. No. 60/837,408, filed Aug. 11, 2006, and/or PCT Application No. PCT/US2003/036177 filed Nov. 14, 2003 and published Jun. 3, 2004 as PCT Publication No. WO 2004/047421, which are all hereby incorporated herein by reference in their entireties. The control may include a lens element or optic between the image sensor and the forward scene to substantially focus the scene at an image plane of the image sensor. Optionally, the optic may comprise a wide angle lens that provides a proportionally distributed central portion of the imaged scene while providing classical optical distortion on the periphery of the imaged scene. Optionally, the optic may comprise a non-flat field curvature, which may focus a generally central portion of the imaged scene onto the image sensor, while providing reduced but acceptable focus on the periphery of the imaged scene. The imaging device may comprise an image sensing module or the like, and may utilize aspects described in U.S. patent application Ser. No. 10/534,632, filed May 11, 2005 and published Aug. 3, 2006 as U.S. Patent Publication No. US-2006-0171704; and/or PCT Application No. PCT/US2006/041709, filed Oct. 27, 2006 and published May 10, 2007 as International Publication No. WO 07/053,404; and/or PCT Application No. PCT/US2003/036177 filed Nov. 14, 2003 and published Jun. 3, 2004 as PCT Publication No. WO 2004/047421, which are hereby incorporated herein by reference in their entireties.

Such imaging sensors or cameras are pixelated imaging array sensors having a photosensing array of a plurality of photon accumulating or photosensing light sensors or pixels, which are arranged in a two-dimensional array of rows and columns on a semiconductor substrate. The camera established on the substrate or circuit board includes circuitry that is operable to individually access each photosensor pixel or element of the array of photosensor pixels and to provide an output or image data set associated with the individual signals to the control, such as via an analog to digital converter. As the camera receives light from objects and/or light sources in the target scene, the control may then be operable to process the signal from at least some of the pixels to analyze the image data of the captured image, as discussed below.

Optionally, the imaging sensor may be suitable for use in connection with other vehicle imaging systems, such as, for example, an object detection system or blind spot detection system, where a blind spot indicator may be operable to provide an indication to the driver of the host vehicle that an object or other vehicle has been detected in the lane or area adjacent to the side of the host vehicle. In such a blind spot detector/indicator system, the blind spot detection system may include an imaging sensor or sensors, or ultrasonic sensor or sensors, or sonar sensor, or radar, or LIDAR or sensors or the like. For example, the detection system may utilize aspects of the detection and/or imaging systems described in U.S. Pat. Nos. 7,038,577; 6,882,287; 6,198,409; 5,929,786; and/or 5,786,772, and/or U.S. patent application Ser. No. 11/315,675, filed Dec. 22, 2005 and published Aug. 17, 2006 as U.S. Publication No. US-2006-0184297; and/or Ser. No. 11/239,980, filed Sep. 30, 2005, now U.S. Pat. No. 7,881,496, and/or U.S. provisional application Ser. No. 60/696,953, filed Jul. 6, 2006; Ser. No. 60/628,709, filed Nov. 17, 2004; Ser. No. 60/614,644, filed Sep. 30, 2004; and/or Ser. No. 60/618,686, filed Oct. 14, 2004, and/or of reverse or backup aid systems, such as the rearwardly directed vehicle vision systems described in U.S. Pat. Nos. 5,550,677; 5,760,962; 5,670,935; 6,922,292; 6,590,719; 6,201,642; 6,396,397; 6,498,620; 6,717,610; 6,757,109; and/or 7,005,974, and/or of the rain sensors described in U.S. Pat. Nos. 6,250,148 and 6,341,523, and/or of other imaging systems, such as the types described in U.S. Pat. Nos. 7,123,168; 6,353,392; and/or 6,313,454, with all of the above referenced U.S. patents, patent applications and provisional applications and PCT applications being commonly assigned and being hereby incorporated herein by reference in their entireties.

In order to enhance the driver's understanding of what is occurring in the area surrounding the vehicle, the rearview vision system includes a display device or display element having image enhancements (FIG. 3). The display device may comprise any suitable display device or element, such as a video display screen, such as a video display screen utilizing aspects of the display devices described in U.S. Pat. Nos. 5,530,240; 6,329,925; 7;370,983; 7,274,501; 7,255,451; 7,195,381; 7,184,190; 6,690,268; 5,668,663 and/or 5,724,187, and/or in U.S. patent application Ser. No. 10/538,724, filed Jun. 13, 2005 and published Mar. 9, 2006 as U.S. Publication No. US 2006-0050018; Ser. No. 11/226,628, filed Sep. 14, 2005 and published Mar. 23, 2006 as U.S. Publication No. US 2006-0061008; Ser. No. 10/993,302, filed Nov. 19, 2004, now U.S. Pat. No. 7,338,177; and/or Ser. No. 11/520,193, filed Sep. 13, 2006, now U.S. Pat. No. 7,581,859; and/or PCT Application No. PCT/US03/29776, filed Sep. 9, 2003 and published Apr. 1, 2004 as International Publication No. WO 2004/026633; and/or PCT Application No. PCT/US03/35381, filed Nov. 5, 2003 and published May 21, 2004 as International Publication No. WO 2004/042457; and/or PCT Application No. PCT/US2006/018567, filed May 15, 2006 and published Nov. 23, 2006 as International Publication No. WO 2006/124682; and/or PCT Application No. PCT/US2006/042718, filed Oct. 31, 2005 and published May 10, 2007 as International PCT Publication No. WO 2007/053710; and/or PCT Application No. PCT/US03/40611, filed Dec. 19, 2003 and published Jul. 15, 2004 as International Publication No. WO 2004/058540, which are all hereby incorporated herein by reference in their entireties.

In the illustrated embodiment, the image enhancements of the imaging system and/or display device include graphic overlays 20 a, 20 b which are lines or segments intended to illustrate to the driver the anticipated path of rearward movement of the vehicle based on the present trajectory of the vehicle. In the illustrated embodiment of FIG. 3, the graphic overlays 20 a, 20 b indicate the anticipated vehicle motion as a function of the vehicle direction of travel as well as the rate of turn of the vehicle. Optionally, the displayed image may have a textual message 20 c alerting the driver of a detected object or otherwise instructing the driver during the rearward maneuver.

The forward or rearward direction of vehicle travel is determined in response to the operator placing the gear selection device (not shown) in the reverse gear position. The degree of turn of the vehicle may be determined by monitoring the movement of the vehicle steering system, monitoring the output of an electronic compass, or monitoring the vehicle differential drive system or the like. Optionally, and desirably, if the vehicle is not in reverse gear position, the graphic overlays are not presented. The imaging system and graphic overlays may utilize aspects of the systems described in U.S. Pat. Nos. 5,670,935; 5,949,331; 6,222,447; and 6,611,202, which are hereby incorporated herein by reference in their entireties. Optionally, the graphic overlays may be static overlays (in other words, graphic overlays that extend generally rearwardly toward a focal point of expansion rearward of the vehicle and that are not dependent on a steering wheel angle or the like), while remaining within the spirit and scope of the present invention.

Optionally, and as shown in FIG. 4, the graphic overlays 30 a, 30 b may function to enhance the driver's awareness of an object detected rearward of the vehicle when the vehicle is shifted into a reverse gear. Optionally, the graphic overlays may include a centrally located overlay 30 c, such as a dashed line or the like, that extends upward toward the focal point of expansion of the displayed image. In the illustrated embodiment, each graphic overlay 30 a, 30 b may be provided in three different colors, such as a green segment 32, a yellow segment 34 and a red segment 36, with the upper or further out segment 32 being green (or other suitable color or pattern), the middle segment 34 being yellow (or other suitable color or pattern), and the closest or lowest segment 36 being red (or other suitable color or pattern). The individual segments may be activated or overlaid in response to a detection of an object rearward of the vehicle and a detected or determined distance between the rear of the vehicle and the detected object.

For example, the rearward imaging system of the present invention may include an imaging sensor for capturing images in a rearward field of view and a display for displaying the images. The system may include or may operate in conjunction with an object detection system for detecting objects rearward of the vehicle and in the path of the vehicle when the vehicle is traveling in reverse (such as, for example, an ultrasonic sensing system, a lidar sensing system or a radar sensing system or via image processing of the captured images or the like). When the vehicle is reversing and no object is detected by the object detection system (or if an object is detected that is further away from the vehicle than a predetermined threshold distance), the graphic overlay or overlays may not be displayed or may be displayed as non-colored or dark or neutral lines or continuous segment or the like (such as similar to the graphic overlays 20 a, 20 b shown in FIG. 3). As the vehicle approaches the object so that the object is detected by the object detection system (or when a detected object is within a first threshold distance from the rear of the vehicle but outside of a second threshold distance from the rear of the vehicle), the outer graphic overlay segment 32 may flash or may be displayed as green to alert the driver of the presence of the object, while also notifying the driver that the object is still a safe distance rearward of the vehicle. As the vehicle further approaches the object (for example, when the object is within the second threshold distance from the rear of the vehicle but outside of a third threshold distance from the rear of the vehicle), the middle graphic overlay segment 34 may flash or may be displayed as yellow to alert the driver that the vehicle is approaching the object. As the vehicle further approaches the object (for example, when the object is within the third threshold distance from the rear of the vehicle), the inner graphic overlay segment 36 may flash or may be displayed as red to alert the driver that the vehicle is very near to the object.

Optionally, the system may also provide a tone or audible alert when the vehicle and object are within the third threshold separation distance or when the vehicle and object are less than a fourth threshold distance apart to further alert the driver that the object is very near to the vehicle and that the driver should not back up any further. Optionally, the graphic overlays may also or otherwise vary in shape or pattern or thickness or color to enhance the driver's cognitive awareness of the location of and distance to a detected object rearward of the vehicle. Optionally, as one segment is activated or colored (as the object is detected within the respective range from the rear of the vehicle), the other segment or segments may be deactivated or de-colored, so that the driver can readily discern that the object is detected within the particular range encompassed by the currently activated or colored graphic overlay segments.

Optionally, the graphic overlay may be designed to assist colorblind drivers to distinguish the color segments of the overlay. A majority of the colorblind population are “red-green colorblind” and have problems in either in the red or green opsin gene. For example, people with a mutant red opsin gene are called “protanopes”, while people with a mutant green opsin gene are called “deuteranopes”. It is estimated that for males, about 8 percent of Caucasians, about 5 percent of Asians and about 4 percent of Africans are “red-green” colorblind. Color blindness is typically sex-linked, so a reduced number of females are colorblind. Red-green color blind people have difficulty distinguishing colors between red and green with similar intensity or brightness. To address this problem, for example, the graphic overlays of the present invention may replace the red colored segment or segments in the overlay graphics with a reddish purple or vermilion colored segment or segments, and may replace the green colored segment or segments with a blue or bluish green segment or segments. Such colors may be recognized and discerned by a typical red-green colorblind person (the yellow colored segments may remain yellow since typical red-green colorblind people would be able to recognize and discern the yellow colored segments). Optionally, different textural features or patterns (such as different stippling or cross-hatching or different degrees of transparency or translucency of the segments or the like) can be used to assist colorblind drivers to distinguish different segments of the graphic overlay.

Optionally, the different colors or features or patterns of the segments may be selectively provided in response to the user or driver selecting the desired or appropriate graphic overlay display scheme. For example, a software or hardware toggle switch or other suitable user actuatable input (such as a button or a voice recognition system or the like) may be implemented to allow the user or driver of the vehicle to select a suitable overlay color scheme, such as a display displaying normal colored graphic overlays for non-colorblind drivers or a display displaying modified graphic overlays (such as a different color scheme or a different texture or pattern scheme or the like) for colorblind drivers. The switch may offer different choices for the user, such as a color scheme for a red-green colorblind person or a different color scheme for other types of colorblindness (whereby the system adjusts the color scheme of the graphic overlays accordingly).

Optionally, and with reference to FIGS. 5-14, the present invention provides a graphic overlay to assist the driver of the vehicle to back up to a trailer hitch or the like. Optionally, and desirably, the camera or image sensor at the rear of the subject vehicle may be offset from the centerline of the vehicle and angled so as to have its field of view be generally rearward and toward the centerline of the vehicle. Such a camera orientation allows for a three-dimensional or perspective image of a trailer hitch alignment graphic overlay that may be imaged so as to appear to extend rearward from the rear of the vehicle and generally along the centerline of the vehicle.

For example, and as shown in FIG. 5, a graphic overlay includes a pair of sideward overlays 130 a, 130 b and a generally centrally located trailer hitch alignment overlay 130 c. The side overlays 130 a, 130 b may be substantially similar to the side overlays 30 a, 30 b, discussed above, and may have colored segments and the like, such that a detailed discussion of the side overlays need not be included herein. The hitch alignment overlay 130 c is generally at or near the center of the displayed image and extends upward toward the focal point of expansion of the displayed image. The side overlays 130 a, 130 b may function as described above, and may be activated or generated or displayed when the vehicle is shifted into reverse, while the hitch alignment overlay 130 c may be similarly activated or generated or displayed, or may be activated or generated or displayed in response to a user input, such as a control input or button or the like that is activated by the driver of the vehicle when the driver is about to back up the vehicle to a trailer (or may be automatically activated or generated or displayed in response to the system detecting or identifying a trailer rearward of the vehicle when the vehicle is traveling in reverse), while remaining within the spirit and scope of the present invention.

As can be seen in FIG. 5, the displayed image is captured by an image sensor that is offset from the centerline of the vehicle and is directed rearward and toward the centerline of the vehicle. In the illustrated embodiment, image sensor is disposed about 305 mm offset from the centerline of the vehicle at about 875 mm above the ground and oriented at an angle of about 40 degrees toward the centerline of the vehicle. The hitch alignment overlay 130 c is displayed as a three-dimensional shape that extends upward in the image and generally along the centerline of the vehicle and toward the focal point of expansion of the camera. The hitch alignment overlay 130 c is generated so as to appear to be a three dimensional object at the rear of the vehicle (such as an object or alignment element having a height of about 440 mm or thereabouts to approximate a height of a hitch of the vehicle). Thus, the alignment overlay provides two planes, one generally at the ground level and one generally at a typical trailer hitch height.

Other mounting locations and angles for the camera and/or other dimensions of the graphic overlays may be implemented without affecting the scope of the present invention. Because the camera is preferably disposed at a height greater than the virtual height of the alignment element/overlay, the displayed image provides a perspective view rearward and downward toward the three dimensional alignment overlay so that the driver can readily discern and understand the alignment overlay to assist the driver in reversing the vehicle toward a trailer hitch of a trailer or the like. The alignment overlay and the offset camera thus provide a scaled and distorted three dimensional image to provide the driver improved depth perception for driving the vehicle toward the trailer or other targeted object.

In the illustrated embodiment of FIG. 5, alignment overlay 130 c is a wire frame or line drawing or representation of a perspective view of a three dimensional rectangular form. However, other shapes or forms may be utilized to provide the desired perspective or view to the driver to assist the driver in reversing the vehicle toward a trailer hitch or other object. For example, and as shown in FIG. 6, the side overlays 130 a′, 130 b′ may be similar to side overlays 130 a, 130 b, discussed above, while the alignment overlay 130 c′ may be a solid or colored three dimensional rectangular form to further enhance the viewability and discernability of the alignment overlay to the driver of the vehicle. Optionally, for example, and as shown in FIG. 7, the side overlays 230 a, 230 b may be similar to side overlays 130 a, 130 b, discussed above, while the alignment overlay 230 c may be a generally planar, two dimensional rectangular form (such as only the upper portion or surface of the three dimensional rectangular form of alignment overlay 130 c, discussed above), which may be a wire form representation (as shown in FIG. 7), or the alignment overlay 230 c′ may be a solid or colored representation (as shown in FIG. 8), depending on the particular application and desired appearance of the alignment overlay in the displayed image. Optionally, and as shown in FIG. 9, the side overlays 330 a, 330 b may be similar to side overlays 130 a, 130 b, discussed above, while the alignment overlay 330 c may be a prism or wedge shaped form having an upper surface (such as a surface or portion similar to the upper region of the alignment overlay 130 c, discussed above) and a shape that tapers or narrows downward to generally a pointed or narrowed lowered portion, to further enhance the perspective view of the alignment overlay. The alignment overlay 330 c may be colored or shaded or solid (as shown in FIG. 9), or may be a wire form representation or the like, without affecting the scope of the present invention.

Optionally, the side overlays may also be represented or generated or displayed three dimensionally to further assist the driver of the vehicle during the rearward maneuver. For example, and as shown in FIG. 10, the side overlays 430 a, 430 b may appear as three dimensional colored or shaded or solid “walls” extending rearward from the vehicle to assist the driver in guiding or driving the vehicle toward the trailer or targeted object. The side overlays 430 a, 430 b may be otherwise similar to side overlays 30 a, 30 b, and may have colored segments 432, 434, 436 or the like, such as discussed above (optionally, the alignment overlay 430 c may be similarly colored or patterned if desired). Optionally, and as shown in FIG. 11, the side overlays 430 a′, 430 b′ and alignment overlay 430 c′ may be displayed as wire frame representations and/or as partially transparent colored representations so as to provide the desired color and enhanced viewability and discernability while limiting or reducing any potential interference with the driver's view of other objects in the displayed image. Optionally, and as shown in FIG. 12, the side overlays 430 a″, 430 b″ and alignment overlay 430 c″ may be displayed as wire frame representations and/or as partially transparent colored representations, while the side overlays 430 a″, 430 b″ may include a lower portion that is substantially similar to side overlays 30 a, 30 b to further enhance the viewability and discernability of the side overlays while limiting or reducing any potential interference with the driver's view of other objects in the displayed image. Optionally, and as shown in FIG. 13, the side overlays 430 a′″, 430 b′″ and alignment overlay 430 c′″ may be displayed as wire frame representations and/or as partially transparent colored representations, while the side overlays 430 a′″, 430 b′″ may include a lower portion that is substantially similar to side overlays 30 a, 30 b and an upper portion that is also colored or shaded to generally correspond with the lower portion of the side overlays, in order to provide enhanced viewability and discernability of the side overlays while further limiting or reducing any potential interference with the driver's view of other objects in the displayed image. Optionally, and as shown in FIG. 14, the side overlays 530 a, 530 b may have an upper portion 531 a and a lower portion 531 b similar to side overlays 430′″, 430″, but may not have the wire form or shaded region therebetween. The upper and/or lower portions 531 a, 531 b of side overlays 530 a, 530 b may have colored segments to assist in indicating a distance to the targeted object. Optionally, and as also shown in FIG. 14, the hitch alignment overlay 530 c may comprise a two dimensional rectangular form (either shaded or colored or wire form), such as described above. Although several optional configurations and combinations of side overlays and center hitch alignment overlays are shown in FIGS. 4-14, clearly other combinations and configurations may be implemented while remaining within the spirit and scope of the present invention.

The side overlays and the alignment overlay may be static overlays or may be adjusted or curved or reconfigured (such as in response to a steering wheel angle of the vehicle or the like) to provide a dynamic overlay when the vehicle is being driven in reverse toward the trailer or targeted object. The side overlays and the centrally located alignment overlay may be activated or generated or displayed in response to a user input, such as a button or other control input that is activated by the driver of the vehicle when it is desired to back up the vehicle toward a targeted object or trailer hitch. Optionally, for example, the displayed image may be activated in response to the vehicle being shifted into reverse and may include side overlays 30 a, 30 b (discussed above), and may provide the three dimensional side overlays and the centrally located hitch alignment overlay in response to the user input. The side overlays and/or the centrally located hitch alignment overlays may be displayed in different colors or different intensities or may be intermittently displayed or the like based on a distance between the vehicle and the trailer hitch or targeted object, such as discussed above with respect to side overlays 30 a, 30 b, while remaining within the spirit and scope of the present invention.

Thus, the imaging system and graphic overlays of the present invention provide enhanced cognitive awareness by the driver of any objects detected rearward of the vehicle when the vehicle is shifted into a reverse gear and as the driver drives the vehicle in a reverse direction. The change in color or change in intensity or intermittent actuation of the graphic overlays on a segment-by-segment basis provides both a spatial cue to the driver of the presence of and proximity of an object rearward of the vehicle and a spectral cue to the driver of the presence of and proximity of an object rearward of the vehicle, so that the driver is readily aware of an object that is detected rearward of the vehicle and is readily aware of the proximity of the detected object to the rear of the vehicle. The centrally located hitch alignment overlay further enhances the discernability of the location of trailer hitch or targeted object to further assist the driver in maneuvering the vehicle in a rearward direction toward the trailer hitch or targeted object.

Optionally, and preferably, the image sensor includes or utilizes a wide angle lens that focuses a wide angle rearward field of view (such as a wide angle field of view of preferably greater than 120 degrees wide and more preferably greater than 135 degrees wide and more preferably at least about 145 degrees wide) onto an image plane of the image sensor. The wide angle lens preferably comprises a multi-element lens having multiple lens optics or elements, such as seven optics arranged along an optic path to focus the rearward wide angle field of view at the imaging plane while reducing distortion of the focused image. For example, the wide angle lens may include seven optic elements, with some of the elements being glass elements (such as an outer wide angle element being a glass element) and some of the elements being plastic elements. Preferably, at least one of the optic elements comprises a plastic aspheric element, and more preferably, two of the optic elements comprise plastic aspheric elements and five of the optic elements comprise glass spherical elements. Such a lens assembly may utilize aspects of the lenses described in U.S. Pat. Nos. 6,922,292; 6,757,109; 6,590,719; and 6,201,642, which are hereby incorporated herein by reference in their entireties.

The lens of the present invention thus may have at least one plastic element, which may provide a cost savings and a reduction in overall lens length. The refractive or diffractive lens element or elements may be made by injection molding or other low cost means. The plastic lens elements may comprise a polycarbonate material or acrylic material or any other suitable plastic or polymeric material. The lens includes non-spherical, refractive or diffractive optic elements, and may have a stop or aperture within the lens to correct distortion in the focused image.

For example, a lens assembly may be provided that is approximately 25 to 26 mm in overall length (from the image plane to the outer end of the lens assembly. The lens elements may be provided in a housing or barrel (such as an aluminum barrel) that may be threaded onto the circuit board that has the image sensor established thereon or threaded onto a housing or mounting portion of an image sensor module. The lens may have a cap diameter of about 12 mm to about 23 mm, with about a 1.0 to 2.5 mm radius on the outer most edge of the lens cap. The lens may provide a wide angle field of view of about 130 degrees in the horizontal and about 105 degrees vertical when the image sensor and lens are mounted at the vehicle, and may have an active sensor area having about a 3.584 mm horizontal dimension and about a 2.688 mm vertical dimension and about a 4.480 diagonal dimension.

The image sensor may comprise a pixelated image sensor (such as a CMOS sensor or the like) having a 640×480 array (or other size array depending on the particular application) of pixels that are about 5.6 μm×5.6 μm. The lens may provide an “F-stop” of about 2.0 (or lower) +/−5 percent, and may have a relative illumination at greater than 50 percent at full field. Preferably, the lens provides a reduced or lowered optical distortion (geometrical), preferably better than about −45 percent. The lens may have a modulation transfer function (a measurement of lens resolution quality) of greater than about 0.6 at 45 lp/mm on lens axis (zero degrees) and greater than about 0.25 at 45 lp/mm off-axis (between zero degrees and 60 degrees).

The lens preferably includes an integrated infrared (IR) cutoff coating or filter that provides about 85 percent or greater transmission of light therethrough over the visible spectrum (about 400 nm to about 700 nm) of light, and about 50 percent or lower transmission of light therethrough for light having wavelengths greater than about 700 nm and less than about 400 nm. The lens may provide a wide angle field of view and may be able to focus on an object within about 30 cm or thereabouts from the outer end of the lens. The lens preferably has an anti-reflective (AR) coating on at least some of the surfaces of the optic elements and preferably on all of the surfaces of the optic elements. The lens may have a variation of effective focal length of less than +/−5 percent. The lens preferably has an image circle diameter of greater than about 4.8 mm and the angle between the lens' optical axis and a barrel reference diameter axis is preferably less than about 1.5 degrees.

The lens is robust and capable of withstanding the extreme climate and environmental conditions that it may encounter at the exterior portion of a vehicle. For example, the lens may be operational at up to about 85 degrees Celsius, and may be able to withstand exposure up to 125 degrees Celsius. The lens is capable of withstanding high temperature and high humidity endurance tests and can withstand exposure at 95 degree Celsius and 85 percent relative humidity for 1200 hours or more. The lens is also capable of withstanding mechanical shock tests (such as 6 shock pulses with 100 g and 10 ms half-sine pulses, one in each opposite direction of three perpendicular axes) and vibration tests (such as a vibration test of an RMS acceleration value of about 27.8 m/s² for about 27 hours in the x-axis, about 27 hours in the y-axis and about 81 hours in the z-axis. Because the outer optic element is exposed to harsh conditions at the rear of the vehicle, the lens comprises a sealed lens and is capable of passing the required OEM testing, such as a car wash spray test and a heavy splash shower test and a mist test and a salt mist test and a dust test and the like. The lens can also withstand a dunk or soak test where the lens is soaked in 95 degrees Celsius water for at least 1 hour and then the upper body of the lens is dunked or soaked in icy water at a depth of 15 cm for at least 30 minutes. The lens is also capable of withstanding exposure to various chemicals. For example, the outer glass surface of the lens and the outer exterior body of the lens may be resistant to automatic transmission fluid, hypoid lubricant, hydraulic fluid, power steering fluid, differential lubricant, central hydraulic fluid, engine oil, engine wax protective, engine coolant/Ethylene Glycol, gasoline, diesel fuel, kerosene, bio-diesel/Methanol based fuel, brake fluid, windshield washer fluid, window glass cleaner, car wash cleaner/soap solution, car wax and silicone protectants, leather wax, battery acid—dilute sulfuric acid, and calcium chloride, and/or other chemicals the lens may encounter at the vehicle assembly plant and/or during its life on the vehicle.

Because the outer glass optic of the lens assembly is positioned toward an exterior of the vehicle such that an outer surface of the outer glass optic may be exposed to the elements outside of the vehicle, the outer surface may be coated with a protective coating to protect the outer optic from deterioration or damage due to exposure to the elements. Such a protective coating may comprise an organic haricot, an inorganic haricot, or an organic/inorganic compound or the like. Additionally, the protective coating may include ultraviolet absorbers or stabilizers to protect the outer optic from UV radiation degradation. Such a coating or other additional coating or coatings substantially reduces the susceptibility of the outer optic to abrasion and/or ultraviolet degradation, thereby providing a substantially clear and durable glass-like appearance to the outer optic. Optionally, the hard coating or protective coating may be of the type described in EPC Application No. 98650039.5, published on Jan. 20, 1999 under Publication No. EP 0892209, the disclosure of which is hereby incorporated herein by reference in its entirety.

Optionally, the outer optic may be heatable to defog or defrost its surfaces. For example, the outer optic may be formed by a glass material and coated with a transparent conductive coating (such as an indium tin oxide (ITO) transparent conductor or a doped tin oxide or the like), or may include a wire mesh or a conductive coating mesh or the like, whereby heat is generated by energizing the conductive coating or mesh via a power source. Optionally, the outer surface of the outer optic may be coated with an anti-soiling or anti-wetting coating, such as a silicone material, which may provide either a hydrophobic or hydrophilic property to the exposed outer surface of the outer optic.

Optionally, the lens body (barrel and optic elements) may be heated electrically to limit or substantially preclude moisture from being trapped inside the lens from condensation. When the lens is assembled in an environment that humidity/moisture level is not tightly controlled below a certain level, the air packet between optic elements inside the lens typically has water molecules in the form of moisture. When the lens is exposed to a temperature that is lower than the dew point temperature of the moisture density level, moisture condensation occurs within the lens, and a small cluster of water droplets may form on the surfaces of the optic elements inside the lens. The condensation or water droplets may blocks or attenuate light passing through the lens and thus may degrade the lens and furthermore may reduce or impair the camera performance. In some situations, the condensation water may drop onto the camera circuitry or circuit board or PCB and may cause an electrical malfunction or electrical shortage. Optionally, a means for measuring the temperature of the lens, such as a temperature sensor, such as a thermal couple or the like, may be used to determine the temperature at or within the lens, while a control means may be responsive to the temperature signal and may activate a heating current or voltage at or in the lens to heat the lens or lens elements above a threshold level in response to a detection or determination that the temperature at or in or of the lens is dropping below the dew point level. Thus, the lens or lens elements may be heated to remain above the dew point temperature so as to limit or substantially avoid moisture condensation from occurring within the lens.

Optionally, a lens body may be filled with a gas that is without water moisture. For example, a dry air, nitrogen gas or helium gas (or other suitable non-moisture gas or air) can be filled inside the lens body. The lens is then sealed to keep the moisture from getting inside lens from outside. The lens can be assembled in an enclosed environment that is filled with the gas without water moisture, such as a dry air, nitrogen or helium gas or the like. Optionally, another means for addressing the moisture issue may provide breathing paths within the lens. For example, the lens body can be designed to have one or more breathing paths by which air and water molecules can travel from all of the inside cavities of the lens to the outside of the lens, such as through the lens bottom or other body wall or housing wall. Optionally, by providing some moisture absorbing material inside the camera cavity, the water molecules that may originally exist inside the lens body can be absorbed by the moisture absorbing material.

The wide angle lens includes corrective refractive and diffractive elements positioned along the optic path between the wide angle outer optic and the image sensor. Additional corrective elements may also be included to further correct color or distortion within the refracted image. Diffractive elements are preferably included to correct the color focusing within the refracted image. The diffractive element or elements may further include an aspheric refractive optic element attached thereto or on an opposite surface of a respective optic element to further correct for distortions and aberrations within the focused image. Optionally, these refractive optic elements may be transparent plastic optic elements, having a varying width, such that the image passing through the refractive lens is refracted in varying degrees, corresponding to the magnitude of distortion in the image received by the refractive optics. Therefore, either by themselves, or in conjunction with the image sensor and/or image processing of the captured images, the refractive and/or diffractive optic elements of the lens function as a means for correcting distortions within the image.

The image system may further reduce image distortion via other distortion reducing means, such as by utilizing non-uniformly distributed pixels at the image array sensor (as discussed below), or such as via an on-imager processing unit (such as a system on chip or the like), such as an FPGA, CPLD, DSP, microprocessor or the like, and associated software, or such as via display means where the distortion correction is done in the displayed image via a non-uniformly distributed pixelated array of the display or via image processing hardware or software of the display device or module.

It is further envisioned that the wide angle imaging system may include electronic image processing or distortion correction to further correct the image displayed on the display. The distortion correction process may be performed by an image processing algorithm or by pixel distribution variation on image capture device and/or an associated display. Preferably, the system may display a vehicle reference, such as a rear bumper of the vehicle, as is seen outside the vehicle, so as to provide a sense of correctness to the image displayed to the driver. For example, an image processing algorithm may be provided which ensures that straight horizontal and/or vertical lines in the scenic information exteriorly of the vehicle are displayed as straight horizontal and/or vertical lines in the image displayed on the display. Such processing allows the imaging system to implement the wide angle lens and still provide a substantially realistic display image to the driver.

Optionally, the image sensor and/or image processing of the captured images may be capable of reducing distortion of the captured image. Such distortion reduction may be accomplished by a non-uniform array of photosensing pixels of the image sensor, such as described in U.S. Pat. No. 5,796,094, which is hereby incorporated herein by reference in its entirety. The non-uniform array may have a coarse distribution of pixels in a center region, with a finer distribution of pixels along the perimeter regions of the captured image. Such non-uniform pixelation of the imaging array receives the focused image and varies correspondingly with the magnitude of distortion in the image refracted through the lens.

Optionally, the image system of the present invention may provide correction of image perspective distortion. Image distortion from the camera with a wide angle lens includes not only lens geometrical distortion (such as pincushion and barrel distortions), but also perspective distortion, which is caused not by lens distortion, but rather is a perspective distortion whereby an object appears in different sizes when it is located at different distances from the camera. This type of distortion may also be corrected via one or more refractive and/or diffractive optic elements of the lens so as to function as lens-based means for correcting distortion. Optionally, the distortion may also or otherwise be corrected via an imager-based means, image processing means and/or display means for correcting distortion, such as those described above.

Optionally, the graphic overlays may be superimposed or projected onto the displayed image based on the image distortion. For example, the system may change or adjust the graphic overlay projection (such as the angle, curvature, thickness, length and/or other characteristics of the lines or overlays) of an overlay pattern in accordance with the position of the overlay pixel at the displayed image.

Thus, the wide angle rearward image system of the present invention provides a wide angle rearward field of view with reduced distortion to the driver of the vehicle so that the images displayed to the driver are readily recognized by the driver when the driver is reversing the vehicle. The image system preferably provides graphic overlays to further enhance the driver's cognitive awareness of detected objects rearward of the vehicle. Although described as a rearward facing imaging system, aspects of the present invention are equally suited for other imaging systems of vehicles, such as side object detection systems or blind spot detection systems or forward facing imaging systems, such as lane departure warning systems and/or the like.

Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention, which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents. 

1. An imaging system for a vehicle, said imaging system comprising: an imaging sensor, wherein said imaging sensor comprises a two-dimensional array of light sensing photosensor elements, and wherein said imaging sensor has a rearward field of view when mounted at a vehicle equipped with said imaging system; a display device comprising a video display screen for displaying images representative of image data captured by said imaging sensor; wherein said imaging system generates an overlay that is electronically superimposed on said displayed images to assist a driver of the equipped vehicle when executing a backup maneuver, said overlay comprising first, second and third overlay zones; wherein said first overlay zone is indicative of a first distance range from the rear of the equipped vehicle to a first distance from the rear of the equipped vehicle as displayed at said video display screen; wherein said second overlay zone is indicative of a second distance range from the first distance to a second distance from the rear of the equipped vehicle as displayed at said video display screen; wherein said third overlay zone is indicative of a third distance range beyond the second distance from the rear of the equipped vehicle as displayed at said video display screen; wherein, as indicated to the driver viewing said video display screen when executing a backup maneuver, the first distance is closer to the rear of the equipped vehicle than the second distance and the second distance is closer to the rear of the equipped vehicle than the third distance; wherein said first overlay zone comprises a first color and said second overlay zone comprises a second color and said third overlay zone comprises a third color; and wherein said first color is a different color than said second color and said second color is a different color than said third color.
 2. The imaging system of claim 1, wherein the color of said first, second and third overlay zones is selectively adjustable by the driver of the equipped vehicle.
 3. The imaging system of claim 1, wherein said first color is a red color, said second color is a yellow color and said third color is a green color.
 4. The imaging system of claim 1, wherein said first color is one of a reddish purple color and a vermilion color, said second color is a yellow color and said third color is one of a blue color and a bluish green color.
 5. The imaging system of claim 1, wherein said imaging system adjusts said first overlay zone in response to an object being detected rearward of the equipped vehicle and within a distance threshold from the rear of the equipped vehicle in order to alert the driver of the equipped vehicle of the presence of the detected object.
 6. The imaging system of claim 1, wherein said imaging system adjusts said second overlay zone in response to an object being detected rearward of the equipped vehicle and within a second distance threshold from the rear of the equipped vehicle, and wherein said imaging system adjusts said first overlay zone in response to an object being detected rearward of the equipped vehicle and within a first distance threshold from the rear of the equipped vehicle, and wherein said second distance threshold is a larger distance than said first distance threshold.
 7. The imaging system of claim 1, wherein, as seen by the driver viewing said video display screen when executing a backup maneuver, said overlay comprises a pair of spaced-apart lines extending outwardly generally from the rear of the equipped vehicle and wherein said first overlay zone comprises a first segment of said pair of spaced-apart lines and wherein said second overlay zone comprises a second segment of said pair of spaced-apart lines and wherein said third overlay zone comprises a third segment of said pair of spaced-apart lines.
 8. The imaging system of claim 7, wherein said overlay comprises a first pair of opposing marks where said first overlap zone generally joins with said second overlap zone and wherein said overlay comprises a second pair of opposing marks where said second overlap zone generally joins with said third overlap zone.
 9. The imaging system of claim 7, wherein said overlay comprises a first mark where said first overlap zone generally joins with said second overlap zone and wherein said overlay comprises a second mark where said second overlap zone generally joins with said third overlap zone.
 10. The imaging system of claim 9, wherein said first mark comprises one of said first color and said second color, and wherein said second mark comprises one of said second color and said third color.
 11. The imaging system of claim 10, wherein said first mark extends at least partially between said pair of spaced-apart lines, and wherein said second mark extends at least partially between said pair of spaced-apart lines.
 12. The imaging system of claim 1, wherein at least one of (a) said imaging system generates an alignment overlay that is electronically superimposed on said displayed images to assist the driver of the equipped vehicle to align the equipped vehicle and (b) said imaging system generates an alignment overlay that is electronically superimposed on said displayed images to assist the driver of the equipped vehicle to align the equipped vehicle and wherein said alignment overlay comprises a centrally located overlay extending rearward from a centerline of the equipped vehicle.
 13. The imaging system of claim 12, wherein said first, second and third overlay zones comprise side overlay segments extending upward and inward along respective sides of the displayed image so as to be indicative of segments extending rearward from the sides of the equipped vehicle, and wherein said alignment overlay is viewed by the driver as having a different virtual height dimension than said side overlay segments to enhance the driver's cognitive awareness of said overlay.
 14. The imaging system of claim 1, wherein said imaging sensor is offset from the centerline of the equipped vehicle, and wherein said imaging system generates an alignment overlay that is electronically superimposed on said displayed images to assist the driver of the equipped vehicle to align the equipped vehicle, and wherein said alignment overlay is displayed as a sideward perspective view of a virtual alignment overlay to enhance the driver's cognitive awareness of the alignment overlay.
 15. An imaging system for a vehicle, said imaging system comprising: an imaging sensor, wherein said imaging sensor comprises a two-dimensional array of light sensing photosensor elements, and wherein said imaging sensor has a rearward field of view when mounted at a vehicle equipped with said imaging system; a display device comprising a video display screen for displaying images representative of image data captured by said imaging sensor; wherein said imaging system generates an overlay that is electronically superimposed on said displayed images to assist a driver of the equipped vehicle when executing a backup maneuver, said overlay comprising first, second and third overlay zones; wherein, as seen by the driver viewing said video display screen when executing a backup maneuver, said overlay comprises a pair of spaced-apart lines extending outwardly generally from the rear of the equipped vehicle and wherein said first overlay zone comprises a first segment of said pair of spaced-apart lines and wherein said second overlay zone comprises a second segment of said pair of spaced-apart lines and wherein said third overlay zone comprises a third segment of said pair of spaced-apart lines; wherein said first overlay zone is indicative of a first distance range from the rear of the equipped vehicle to a first distance from the rear of the equipped vehicle as displayed at said video display screen; wherein said second overlay zone is indicative of a second distance range from the first distance to a second distance from the rear of the equipped vehicle as displayed at said video display screen; wherein said third overlay zone is indicative of a third distance range beyond the second distance from the rear of the equipped vehicle as displayed at said video display screen; wherein, as indicated to the driver viewing said video display screen when executing a backup maneuver, the first distance is closer to the rear of the equipped vehicle than the second distance and the second distance is closer to the rear of the equipped vehicle than the third distance; wherein said overlay comprises a first mark where said first overlap zone generally joins with said second overlap zone and wherein said overlay comprises a second mark where said second overlap zone generally joins with said third overlap zone; wherein said first overlay zone comprises a first color and said second overlay zone comprises a second color and said third overlay zone comprises a third color; and wherein said first color is a red color, said second color is a yellow color and said third color is a green color.
 16. The imaging system of claim 15, wherein said first mark comprises one of the red color and the yellow color, and wherein said second mark comprises one of the yellow color and the green color.
 17. The imaging system of claim 16, wherein said first mark extends at least partially between said pair of spaced-apart lines, and wherein said second mark extends at least partially between said pair of spaced-apart lines.
 18. The imaging system of claim 15, wherein at least one of (a) said imaging system generates an alignment overlay that is electronically superimposed on said displayed images to assist the driver of the equipped vehicle to align the equipped vehicle and (b) said imaging system generates an alignment overlay that is electronically superimposed on said displayed images to assist the driver of the equipped vehicle to align the equipped vehicle and wherein said alignment overlay comprises a centrally located overlay extending rearward from a centerline of the equipped vehicle.
 19. The imaging system of claim 18, wherein said alignment overlay is viewed by the driver as having a different virtual height dimension than said first, second and third segments of said pair of spaced-apart lines to enhance the driver's cognitive awareness of said overlay.
 20. An imaging system for a vehicle, said imaging system comprising: an imaging sensor, wherein said imaging sensor comprises a two-dimensional array of light sensing photosensor elements, and wherein said imaging sensor has a rearward field of view when mounted at a vehicle equipped with said imaging system; a display device comprising a video display screen for displaying images representative of image data captured by said imaging sensor; wherein said imaging system generates an overlay that is electronically superimposed on said displayed images to assist a driver of the equipped vehicle when executing a backup maneuver, said overlay comprising first, second and third overlay zones; wherein, as seen by the driver viewing said video display screen when executing a backup maneuver, said overlay comprises a pair of spaced-apart lines extending outwardly generally from the rear of the equipped vehicle and wherein said first overlay zone comprises a first segment of said pair of spaced-apart lines and wherein said second overlay zone comprises a second segment of said pair of spaced-apart lines and wherein said third overlay zone comprises a third segment of said pair of spaced-apart lines; wherein said first overlay zone is indicative of a first distance range from the rear of the equipped vehicle to a first distance from the rear of the equipped vehicle as displayed at said video display screen; wherein said second overlay zone is indicative of a second distance range from the first distance to a second distance from the rear of the equipped vehicle as displayed at said video display screen; wherein said third overlay zone is indicative of a third distance range beyond the second distance from the rear of the equipped vehicle as displayed at said video display screen; wherein, as indicated to the driver viewing said video display screen when executing a backup maneuver, the first distance is closer to the rear of the equipped vehicle than the second distance and the second distance is closer to the rear of the equipped vehicle than the third distance; wherein said overlay comprises a first mark where said first overlap zone generally joins with said second overlap zone and wherein said overlay comprises a second mark where said second overlap zone generally joins with said third overlap; and wherein said first mark extends at least partially between said pair of spaced-apart lines, and wherein said second mark extends at least partially between said pair of spaced-apart lines.
 21. The imaging system of claim 20, wherein at least one of (a) said imaging system generates an alignment overlay that is electronically superimposed on said displayed images to assist the driver of the equipped vehicle to align the equipped vehicle and (b) said imaging system generates an alignment overlay that is electronically superimposed on said displayed images to assist the driver of the equipped vehicle to align the equipped vehicle and wherein said alignment overlay comprises a centrally located overlay extending rearward from a centerline of the equipped vehicle.
 22. The imaging system of claim 21, wherein said alignment overlay is viewed by the driver as having a different virtual height dimension than said first, second and third segments of said pair of spaced-apart lines to enhance the driver's cognitive awareness of said overlay.
 23. The imaging system of claim 20, wherein said overlay comprises a first pair of opposing marks where said first overlap zone generally joins with said second overlap zone and wherein said overlay comprises a second pair of opposing marks where said second overlap zone generally joins with said third overlap zone, and wherein said first pair of opposing marks extends at least partially between said pair of spaced-apart lines, and wherein said second pair of opposing marks extends at least partially between said pair of spaced-apart lines. 